I/O Area; Input Bits - Omron CJ2 CPU UNIT SOFTWARE User Manual

6 I/O Memory Areas
6-2

I/O Area

I/O Area addresses range from CIO 0 to CIO 159 for words and CIO 0.00 to CIO 159.15 for bits.
Words in the I/O Area are allocated to I/O terminals on Basic I/O Units. Words are allocated to Basic I/O
Units based on the slot position (left to right) and number of words required. The words are allocated
consecutively and empty slots are skipped. Words in the I/O Area that aren't allocated to Basic I/O Units
can be used only in the program.
Bits in the I/O Area can be force-set and force-reset.
Note The area can be expanded to CIO 0000 to CIO 0999 by changing the first word allocated to a specific Unit.
The maximum number of bits that can be allocated for external I/O will still be 2,560 (160 words) even if the
I/O Area is expanded.
6-2-1

Input Bits

A bit in the I/O Area is called an input bit when it is allocated to an Input Unit. Input bits reflect the
ON/OFF status of devices such as pushbutton switches, limit switches, and photoelectric switches.
There are three ways for the status of input points to be refreshed in the PLC: normal I/O refreshing,
immediate refreshing, and IORF(097) refreshing.
Normal I/O Refreshing
The status of input points on external devices is read once each cycle after program execution. In
the following example, CIO 1.01 is allocated to switch 1, an external switch connected to the input
terminal of an Input Unit. The ON/OFF status of switch 1 is stored in CIO 1.01 once each cycle.
6-8
Ladder symbol
1.01
Input Unit
Switch 1
Once
each
cycle
Mnemonic
LD 1.01
CPU Unit
Bit allocation
CIO 1.01
CJ2 CPU Unit Software User's Manual